Report on Anatahan (United States) — 14 March-20 March 2007
Smithsonian / US Geological Survey Weekly Volcanic Activity Report, 14 March-20 March 2007
Managing Editor: Sally Kuhn Sennert
Please cite this report as:
Global Volcanism Program, 2007. Report on Anatahan (United States). In: Sennert, S K (ed.), Weekly Volcanic Activity Report, 14 March-20 March 2007. Smithsonian Institution and US Geological Survey.
16.35°N, 145.67°E; summit elev. 790 m
All times are local (unless otherwise noted)
USGS reported that seismicity from Anatahan increased on 24 February and remained elevated through 17 March, occasionally punctuated by higher levels of tremor and increased gas emissions. On 13 March, seismic activity increased significantly; a gas plume that was visible on MODIS satellite imagery suggested increased emissions. The next day the Volcanic Alert Level was increased from Normal to Advisory. On 20 March, low levels of tremor were recorded.
Geologic Background. The elongate, 9-km-long island of Anatahan in the central Mariana Islands consists of a large stratovolcano with a 2.3 x 5 km compound summit caldera. The larger western portion of the caldera is 2.3 x 3 km wide, and its western rim forms the island's high point. Ponded lava flows overlain by pyroclastic deposits fill the floor of the western caldera, whose SW side is cut by a fresh-looking smaller crater. The 2-km-wide eastern portion of the caldera contained a steep-walled inner crater whose floor prior to the 2003 eruption was only 68 m above sea level. A submarine cone, named NE Anatahan, rises to within 460 m of the sea surface on the NE flank, and numerous other submarine vents are found on the NE-to-SE flanks. Sparseness of vegetation on the most recent lava flows had indicated that they were of Holocene age, but the first historical eruption did not occur until May 2003, when a large explosive eruption took place forming a new crater inside the eastern caldera.